When the small Japanese seaside town of Susami needed a tourism boost, an unlikely resident came to the rescue: the town’s postmaster. Together with the local diving community, former postmaster Toshihiko Matsumoto helped establish the world’s first underwater mailbox. Those willing to make the plunge can strap on a wetsuit and mail letters from 30 feet under the sea. Incredibly, dive shop owner Hiroaki Yamatani descends each day to collect and deliver these letters to the post office. To date, almost 38,000 letters have been sent from under the sea.

This story is a part of our Frontiers series, where we bring you front and center to the dreamers, pioneers, and innovators leading society at the cutting edge. Let us take you along for a trip to the oft-imagined but rarely accomplished.

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